The long term objectives are to gain more knowledge about intestinal lymphatic drug absorption, the mechanism(s) and factors that influence drug absorption by this route. Toward this goal, this proposal will investigate the effects of C4-C18 fatty acids (butyric, caprylic, lauric, palmitic, stearic and oleic) on the (a) absorption of cyclosporine by the intestinal lymphatics, (b) distribution of cyclosporine in intestinal lymph, and blood, (c) blood-to-lymph transfer of cyclosporine and (d) accumulation of cyclosporine by lymphoid tissue. The role of chylomicrons in intestinal lymphatic cyclosporine absorption will also be studied. Cyclosporine is a potent and specific immunosuppressive agent. Since the lymphatic system is intimately associated with the immune system, the intestinal lymphatic absorption of cyclosporine would target the drug directly to a site of action. The effects of C4-C18 fatty acids on intestinal lymphatic cyclosporine absorption will be studied in mesenteric lymph cannulated Sprague-Dawley rats after 0.1 and 0.5 mmoles of fatty acid are coadministered with cyclosporine (20 mg/kg) via a duodenal cannula. The extent and accumulation rate of cyclosporine in the lymph after 24 hours will be determined and analyzed by ANOVA. The lymph samples will be ultracentrifuged to separate the chylomicrons. The chylomicron fraction and amounts of cyclosporine in the chylomicron and aqueous fractions will be determined to evaluate (ANOVA) the effects of fatty acids on cyclosporine distribution in intestinal lymph. The role of chylomicrons in lymphatic cyclosporine absorption will be assessed in rats pretreated with colchicine, a substance known to interfere with chylomicron formation. The effects of fatty acids on the blood-to-lymph transfer of cyclosporine will be determined in rats after intravenous bolus cyclosporine injections (3 mg/kg) and fatty acid coadministration intraduodenally. The blood-to-lymph clearance rate as well as the accumulation characteristics of the drug in thoracic duct lymph will be determined. The effects of fatty acids on the binding of cyclosporine to plasma proteins will be determined in vitro by ultrafiltration. The accumulation of cyclosporine in thymus tissue and abdominal lymph nodes will be determined at steady state after 7 days of treatment with cyclosporine (10 mg/kg/day) and fatty acid per os. Blood and lymph samples will be assayed for cyclosporine with a specific HPLC method. Lymph and lymphoid tissue 14C- fatty acid levels will be determined by liquid scintillation counting.